It is often desired to store or transport material while maintaining the material at a cryogenic temperature. Examples include the storage or transport of liquid helium or liquid hydrogen wherein it is desired to maintain the helium or hydrogen in a liquid state. Generally this has heretofore been accomplished by the use of a lower value cryogenic liquid, e.g., liquid nitrogen, to thermoshield the liquid helium or hydrogen and thermostation storage vessel parts. Typically the conventional arrangement comprises a liquid nitrogen tank at one end of the vessel with the nitrogen passed across the vessel through a large number of lines. As the liquid nitrogen passes across the vessel, heat leak into the vessel causes the liquid nitrogen to vaporize and the nitrogen vapor is vented at the other end of the container. In this way heat is kept from the liquid helium or hydrogen in the center of the storage vessel.
A problem with the conventional vessel is inefficient use of the liquid nitrogen. The liquid nitrogen often undergoes vaporization in an agitated state, i.e., is boiled, and this boiling causes liquid nitrogen, in the form of mist or slugs, to pass through the lines without being vaporized. This liquid eventually passes out of the container without a thermoshielding or thermostationing effect.
It is desirable to have a cryogenic storage vessel which can employ cryogenic liquid for thermoshielding and thermostationing purposes wherein all of the liquid refrigerant contributes to the maintenance of cryogenic temperatures.
It is an object of this invention to provide a cryogenic storage vessel and method wherein a cryogenic liquid may be more efficiently employed for thermoshielding and thermostationing purposes.